The extensive evidence that vehicle alcohol interlocks reduce recidivism of driving under the influence (DUI) offenders by two-thirds has resulted in a national effort-led by Mothers Against Drunk Driving and supported by the National Highway Traffic Safety Administration-to encourage all states to enact laws requiring interlocks for all DUI offenders. This, in turn, has led to a rapid growth in the application of these devices; approximately 300,000 interlock devices are currently in use. A major limitation in their effectiveness, however, is that the safety benefit they produce occurs only during the 6- to 12-month period while installed on offenders' vehicles, a relatively short segment of time in which their high-risk driving is controlled compared to the lifetime of driving that follows. There is strong evidence that, during that period on the interlock, most offenders adapt their drinking and driving to avoid being prevented from starting their cars, and that those who do so have lower recidivism following interlock removal. In contrast, those who fail to adapt and continue to have lockouts have greater recidivism following device removal. Thus, an important opportunity exists to create interventions promoting adaptation to the interlock, thereby reducing recidivism and extending benefits. This application takes advantage of a close working relationship between the Pacific Institute for Research and Evaluation and the Florida Department of Highway Safety and Motor Vehicles. This relationship (developed over a decade of research covering 150,000 DUIs) has provided the basis for the department's agreement to assist in our proposed survey of 6oo offenders on their entrance and exit from the interlock program. This exploratory research aims to develop a typology of interlock users that will help program managers predict which offenders will have problems adapting to the interlock and understand how interlock users adapt their drinking and driving behavior to the interlock experience. Ultimately, this information can lead to the development of an intervention designed to help offenders preserve the improved health behaviors adopted while on the interlock device.